Write Set Boundary Management in Support of Asynchronous Update of Secondary Storage

1. A color control node comprising: an interface for communicating with a plurality of primary storage controllers, wherein said plurality of primary storage controllers are operatively coupled with primary storage systems at a primary site; and wherein the plurality of primary storage controllers periodically transmit sets of data writes, known as colors, to secondary storage controllers for writing to secondary storage systems at remote sites; and wherein the primary site operates in a normal operating mode while maintaining a current color and associates all writes with said current color without polling the color control node when maintaining said current color; and wherein the primary site switches to a color polling mode when the current color is to be changed to a new color; wherein the switch to the color polling mode causes a querying of the color control node for every write operation; and wherein the color control node further comprises operational capability for asynchronous updating, said asynchronous updating comprising steps of: responsive to the switch to the color polling mode, issuing a command to instruct the primary storage controllers to poll the color control node for the current color prior to associating each write with said current color; receiving an acknowledgment of receipt of the polling command from all of the primary storage controllers; changing to the new color responsive to the acknowledgment; establishing the new color as the current color; issuing a command to the primary storage controllers indicating the new color as the current color for associating all writes and instructing the primary storage controllers to stop polling the control node for the current color; wherein the primary site then reverts to the normal operating mode, with the primary storage controllers associating all writes with the current color without polling the color control node.

2. The color control node of claim 1 wherein the primary site switches to the color polling mode in accordance with a predefined schedule.

3. A system for maintaining colors and color boundaries across multiple storage controllers, the system comprising: a primary site comprising a plurality of primary storage controllers operatively coupled with primary storage systems, wherein said plurality of primary storage controllers periodically transmit sets of data writes, known as colors, to secondary storage controllers for writing to secondary storage systems at remote sites; and wherein the primary site operates in a normal operating mode while maintaining a current color and associates all writes with said current color without polling a color control node when maintaining said current color; wherein the primary site switches to a color polling mode when the current color is to be changed to a new current color; wherein the primary site polls the color control node subsequent to receiving the instruction to poll said color control node and in response, receives the storage command from the color control node indicating the new current color to associate with all writes; and wherein the primary site reverts to the normal operating mode when at least one of the plurality of primary storage controllers is instructed by the color control node to stop polling the color control node for the current color; and wherein the system further comprises: the color control node operatively coupled with at least one of the plurality of primary storage controllers, said color control node comprising: an interface for communicating with the plurality of primary storage controllers; and operational capability for asynchronous updating comprising steps of: responsive to the switch to the color polling mode, issuing a command to instruct the primary storage controllers to poll the color control node for the current color prior to associating each write with said current color; receiving an acknowledgment of receipt of the command from all of the primary storage controllers; changing to the new color responsive to the acknowledgment; establishing the new color as the new current color; and issuing a command to the primary storage controllers indicating the new color as the current color for associating all writes and instructing the primary storage controllers to stop polling the control node for the current color.

4. The system of claim 3 wherein at least one of the plurality of the primary storage controllers comprise an enterprise storage server.

5. The system of claim 3 wherein at least one of the plurality of the primary storage controllers comprise an array of storage devices.

6. The system of claim 3 wherein the primary storage controllers are operatively coupled with the second storage controllers via a dedicated fiber optical network.

7. The system of claim 3 wherein the primary storage controllers are operatively coupled with the second storage controllers via the Internet.

8. The system of claim 3 wherein the color control node is located at the primary site.

9. The system of claim 8 wherein the color control node is operatively coupled with each of the plurality of primary storage controllers.

10. The system of claim 3 further comprising a plurality of host systems at the primary site, wherein said host systems are operable for communicating with the primary storage controllers.

11. The system of claim 10 wherein the host systems perform input/output operations on data in the primary storage systems.

12. The system of claim 3 wherein the primary site switches to the color polling mode in accordance with a predefined schedule.

13. The color control node of claim 1 wherein the switch to the color polling mode is initiated by said color control node.

14. The color control node of claim 1 wherein the switch to the color polling mode occurs in response to a host system at the primary site starting to poll.

15. The color control node of claim 1 wherein the asynchronous updating further comprises issuing a storage command to the primary storage controllers indicating the new current color after establishing said new color as the current color.